Probe data mapping using contact information

ABSTRACT

A method of mapping includes receiving inputs measured by a probe at respective locations inside a body cavity of a subject. At each of the respective locations, a respective contact quality between the probe and a tissue in the body cavity is measured. The inputs for which the respective contact quality is outside a defined range are rejected, and a map of the body cavity is created using the inputs that are not rejected.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/853,210, filed Apr. 20, 2022, now U.S. Pat. No. 11,369,300, which isa continuation of U.S. patent application Ser. No. 12/633,324 filed Dec.8, 2009, now U.S. patent Ser. No. 10/624,553, the entire content of allof which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to invasive diagnostictechniques, and specifically to mapping of physiological parametersinside the body.

BACKGROUND

A wide range of medical procedures involve placing objects, such assensors, tubes, catheters, dispensing devices, and implants, within thebody. Position sensing systems have been developed for tracking suchobjects. Magnetic position sensing is one of the methods known in theart. In magnetic position sensing, magnetic field generators are placedbelow the patient's torso at known positions external to the patient. Amagnetic field sensor within the distal end of a probe generateselectrical signals in response to these magnetic fields, which areprocessed in order to determine the position coordinates of the distalend of the probe. These methods and systems are described in U.S. Pat.Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. PatentApplication Publications 2002/0065455 A1, 2003/0120150 A1 and2004/0068178 A1, whose disclosures are all incorporated herein byreference.

When placing a probe within the body, it may be desirable to have thedistal tip of the probe in direct contact with body tissue. The contactcan be verified by measuring either the electrical impedance or thecontact pressure between the distal tip and the body tissue. U.S. PatentApplication Publications 2007/0100332, to Paul et al., and 2009/0093806,to Govari et al., for example, describe methods of sensing contactpressure between the distal tip of a catheter and tissue in a bodycavity using a force sensor embedded in the catheter.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a method of mapping,which includes receiving inputs measured by a probe at respectivelocations inside a body cavity of a subject. At each of the respectivelocations, a respective contact quality between the probe and a tissuein the body cavity is measured. The inputs for which the respectivecontact quality is outside a defined range are rejected, and a map ofthe body cavity is created using the inputs that are not rejected.

In a disclosed embodiment, the body cavity includes a chamber of aheart, and receiving the inputs includes receiving signals from aposition transducer in the probe that are indicative of coordinates of adistal end of the probe inside the body cavity.

In some embodiments, receiving the inputs includes measuring aphysiological parameter at the locations, and creating the map includesmapping the physiological parameter over the cavity. Measuring thephysiological parameter may include receiving signals that areindicative of electrical activity in the tissue.

In disclosed embodiments, measuring the respective contact qualityincludes measuring a pressure exerted on a distal end of the probe.Measuring the pressure typically includes receiving a signal from aforce sensor within the probe. Rejecting the inputs may includerejecting measurements when the pressure is below a predetermined lowerbound and/or when the pressure is above a predetermined upper bound. Inone embodiment, the method includes controlling the probe automatically,responsively to the measured pressure, so as to move the probe withinthe body cavity.

In an alternative embodiment, measuring the respective contact qualityincludes measuring an electrical impedance between the probe and thetissue.

In one embodiment, creating the map includes adding tags to the mapindicating the respective contact quality at one or more of thelocations.

There is also provided, in accordance with an embodiment of the presentinvention, apparatus for mapping, including a probe, having a distal endconfigured for insertion into a body cavity and including a contactsensor for measuring a respective contact quality between the probe anda tissue at multiple locations in the body cavity. A console isconfigured to receive inputs from the probe that are indicative of thecontact quality at each of the respective locations, to reject theinputs for which the respective contact quality is outside a definedrange, and to create a map of the body cavity using the inputs that arenot rejected.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a schematic pictorial illustration of a mapping system, inaccordance with an embodiment of the present invention;

FIG. 2 is a schematic side view showing details of the distal portion ofa catheter, in accordance with an embodiment of the present invention;and

FIG. 3 is a flow diagram that schematically illustrates a method ofgated mapping based on contact quality, in accordance with an embodimentof the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In electrophysiological diagnostic procedures using an invasive probe,such as intracardiac electrical mapping, it is important to maintain theproper level of force between probe and tissue. Sufficient force isneeded in order to ensure good electrode contact between the probe andthe tissue. Poor electrical contact can result in inaccurate readings.On the other hand, excessive force can deform the tissue and thusdistort the map. In severe cases, too much pressure may cause physicaldamage to the body cavity wall.

In embodiments of the present invention, acquisition ofelectrophysiological mapping data (i.e., mapping both probe location andelectrical activity in tissue in contact with the probe at the location)is gated so that data points are acquired only when there is adequatecontact between the probe and the tissue. The contact quality (i.e., ameasure of the adequacy of the contact between the probe and the tissue)may be verified by measuring the contact pressure exerted by the probeagainst the tissue, using a force sensor as described furtherhereinbelow. Alternatively, the contact quality may be verified by othermeans, such as measurement of electrical impedance. Map data points areacquired only when the contact quality is within the desired range. Ifthe contact quality is out of range, the operator may be prompted toreposition the catheter.

In the embodiments that are described hereinbelow, contact gating isused in cardiac electrophysiological mapping. Contact gating limits thecollection of map points from the probe to instances in which thecontact quality is within a desired range. The term “map point,” in thecontext of the present patent application and in the claims, refers to aset of location coordinates, possibly together with a signal valuerelating to a physiological parameter at the location of thecoordinates. In embodiments that are described below, the signal valuethat is measured at the map points represents cardiac electricalactivity. This sort of contact gating may be useful particularly, forexample, in conjunction with techniques such as bipolar electricalmapping and local activation time mapping. Alternatively, contact gatingmay be used in mapping of other organs, as well as in mapping of othertypes of physiological parameters. Additionally or alternatively,contact quality information may be added to tags that are associatedwith data points in the map.

Further alternatively, in some cases the location coordinates may beused to create a map without necessarily recording any otherphysiological parameter over the map. For example, the tip of a cathetermay be moved over the inner surface of a heart chamber (or other bodycavity), and data points may be gathered only when the contact pressureis above a certain threshold in order to create a physical map of thesurface. Alternatively, the catheter may be moved within the bodycavity, and data points may be gathered only when the contact pressureis below a certain threshold in order to create a map of the volume ofthe cavity. (This volume map may be converted into a surface map byfinding and linking the outer points of the volume; various methods maybe used for this purpose, such as the ball-pivoting algorithm describedin U.S. Pat. No. 6,968,299, whose disclosure is incorporated herein byreference.)

Measuring contact quality can be performed in a variety of ways. In afirst embodiment, a force sensor may be embedded in the distal portionof a probe. As the probe comes in contact with body tissue, the pressureof the distal tip of the probe against the tissue is transmitted to acontrol unit, which will accept mapping data only if the pressure iswithin a specified range. In an alternative embodiment, a sensor candetect and relay electrical impedance information to the control unit,which will accept the mapping information only if the impedance iswithin a specified range.

FIG. 1 is an illustration of a position sensing system 10, which isconstructed and operative in accordance with a disclosed embodiment ofthe invention. System 10 may be based, for example, on the CARTO™system, produced by Biosense Webster Inc. (Diamond Bar, Calif.). System10 comprises a probe 18, such as a catheter, and a control console 24.In the embodiment described hereinbelow, it is assumed that probe 18 isused in creating electrophysiological maps of one or more heartchambers. Alternatively, probe 18 may be used, mutatis mutandis, forother therapeutic and/or diagnostic purposes in the heart or in otherbody organs.

An operator 16, such as a cardiologist, inserts probe 18 through thevascular system of a patient 14 so that a distal end 20 of probe 18enters a chamber of the patient's heart 12. Operator 16 advances probe18 so that the distal tip of probe 18 engages endocardial tissue at adesired location or locations. Probe 18 is typically connected by asuitable connector at its proximal end to console 24.

Console 24 uses magnetic position sensing to determine positioncoordinates of distal end 20 inside heart 12. To determine the positioncoordinates, a driver circuit 28 in console 24 drives field generators22 to generate magnetic fields within the body of patient 14. Typically,field generators 22 comprise coils, which are placed below the patient'storso at known positions external to patient 14. These coils generatemagnetic fields in a predefined working volume that contains heart 12. Amagnetic field sensor within distal end 20 of probe 18 (shown in FIG. 2)generates electrical signals in response to these magnetic fields. Asignal processor 26 processes these signals in order to determine theposition coordinates of distal end 20, typically including both locationand orientation coordinates. The method of position sensing describedhereinabove is implemented in the above-mentioned CARTO™ system and isdescribed in detail the patents and patent applications cited above.

Processor 26 typically comprises a general-purpose computer, withsuitable front end and interface circuits for receiving signals fromprobe 18 and controlling the other components of console 24. Processor26 may be programmed in software to carry out the functions that aredescribed herein. The software may be downloaded to console 24 inelectronic form, over a network, for example, or it may be provided ontangible media, such as optical, magnetic or electronic memory media.Alternatively, some or all of the functions of processor 26 may becarried out by dedicated or programmable digital hardware components.

An I/O interface 30 enables console 24 to interact with probe 18. Basedon the signals received from probe 18 (via interface 30) and othercomponents of system 10, processor 26 drives a display 32 to presentoperator 16 with a map 34 of cardiac electrophysiological activity, aswell as providing visual feedback regarding the position of distal end20 in the patient's body and status information and guidance regardingthe procedure that is in progress. In the present embodiment, processor26 gates the probe signals, accepting data points for map 34 only whenthe contact force of distal end 20 against the wall of heart 12 iswithin a specified range. In some embodiments of the present invention,display 32 provides visual feedback to operator 16 regarding the contactpressure. If the contact pressure is outside the specified range,operator 16 may be prompted to reposition probe 18.

Alternatively or additionally, system 10 may comprise an automatedmechanism (not shown) for maneuvering and operating probe 18 within thebody of patient 14. Such mechanisms are typically capable of controllingboth the longitudinal motion (advance/retract) of probe 18 andtransverse motion (deflection/steering) of distal end 20 of probe 18. Insuch embodiments, processor 26 generates a control input for controllingthe motion of probe 18 based on the signals provided by the magneticfield sensor in probe 18. These signals are indicative of both theposition of distal end 20 of probe 18 and of force exerted on distal end20, as explained further hereinbelow. Alternatively or additionally, themeasured pressure may be used in automatically controlling the probewithin the body. The pressure measurement can be used both in navigatingthe probe to appropriate mapping locations and to enhance the safety ofthe procedure by preventing the probe from exerting excessive force onthe tissue.

Although FIG. 1 shows a particular system configuration, other systemconfigurations can also be employed to implement embodiments of thepresent invention, and are thus considered to be within the spirit andscope of this invention. For example, the methods described hereinbelowmay be applied using position transducers of other types, such asimpedance-based or ultrasonic position sensors. The term “positiontransducer” as used herein refers to an element mounted on probe 18which causes console 24 to receive signals indicative of the coordinatesof the element. The position transducer may thus comprise a receiver onthe probe, which generates a position signal to the control unit basedon energy received by the transducer; or it may comprise a transmitter,emitting energy that is sensed by a receiver external to the probe.Furthermore, the methods described hereinbelow may similarly be appliedin mapping and measurement applications using not only catheters, butalso probes of other types, both in the heart and in other body organsand regions.

FIG. 2 is a schematic side view of distal end 20 of probe 18, inaccordance with an embodiment of the present invention. Specifically,FIG. 2 shows functional elements of distal end 20 used in creating a mapof cardiac electrical activity. An electrode 40 at a distal tip 46 ofthe probe senses electrical signals in the tissue. Electrode 40 istypically made of a metallic material, such as a platinum/iridium alloyor another suitable material. Alternatively, multiple electrodes (notshown) along the length of the probe may be used for this purpose.

A position sensor 42 generates a signal to console 24 that is indicativeof the location coordinates of distal tip 46. Position sensor 42 maycomprise one or more miniature coils, and typically comprises multiplecoils oriented along different axes. Alternatively, position sensor 42may comprise either another type of magnetic sensor, an electrode whichserves as a position transducer, or position transducers of other types,such as impedance-based or ultrasonic position sensors. Although FIG. 2shows a probe with a single position sensor, embodiments of the presentinvention may utilize probes with more than one position sensors.

In an alternative embodiment, the roles of position sensor 42 andmagnetic field generators 22 may be reversed. In other words, drivercircuit 28 may drive a magnetic field generator in distal end 20 togenerate one or more magnetic fields. The coils in generator 22 may beconfigured to sense the fields and generate signals indicative of theamplitudes of the components of these magnetic fields. Processor 26receives and processes these signals in order to determine the positioncoordinates of distal end 20 within heart 12.

A force sensor 44 senses contact between distal tip 46 and endocardialtissue of heart 12, by generating a signal to the console that isindicative of the pressure exerted by distal tip 46 on the tissue. Inone embodiment, the force sensor may comprise position sensor 42,together with a magnetic field transmitter and mechanical elements indistal end 20, and may generate an indication of the force based onmeasuring the deflection of the distal tip. Further details of this sortof probe and force sensor are described in U.S. Patent ApplicationPublications 2009/0093806 and 2009/0138007, whose disclosures areincorporated herein by reference. Alternatively, distal end 20 maycomprise another type of contact sensor.

FIG. 3 is a flow diagram that schematically illustrates a method ofgated mapping based on contact quality, in accordance with an embodimentof the present invention. After operator 16 positions probe 18 (step50), processor 26 processes the signals generated by a force sensor 44in order to derive a measure of contact quality, such as an indicationof the pressure exerted by a distal tip 46 of probe 18 on endocardialtissue of heart 12 (step 52). Lower pressure means that there may beinadequate contact between electrode 40 at distal tip 46 and theendocardial tissue. Higher pressure may mean that electrode 40 ispressing too hard against the endocardial tissue. Although the exampledescribed here uses pressure to determine contact quality, othermethods, such as measuring electrical impedance, can alternatively beused for this purpose.

If the contact quality is not within a specified range (step 54),console 24 outputs an indication to display 32 of the pressure measuredusing force sensor 44, and may issue an alarm if the pressure is too lowor too high, thereby prompting operator 16 to reposition probe 18 (step56), and the method returns to step 50. For example, when the forceexerted by a catheter tip on the heart wall is 5 grams or more, thecontact quality may be considered sufficient for mapping, while a forceabove 35 grams may be dangerously high. Alternatively or additionally,the pressure indication may be used in closed-loop control of anautomated mechanism for maneuvering and operating probe 18, as describedhereinabove, to ensure that the mechanism causes distal tip 46 of probe18 to engage the endocardium in the proper location, and with theappropriate pressure against the tissue.

Returning to FIG. 3, if the contact quality is within the specifiedrange (step 54), processor 26 collects a map point, including acoordinate reading from position sensor and an electrical signal fromelectrode 40 (step 58), and updates map 34. Finally, if operator 16desires to collect additional mapping data, then the method returns tostep 50 until the map is completed.

Although the operation of position sensor 42 and force sensor 44 isdescribed above in the context of using a catheter for acquisition ofelectrophysiological mapping data, the principles of the presentinvention may similarly be applied in other therapeutic and diagnosticapplications that use invasive probes, both in heart 12 and in otherorgans of the body. For example, the devices and techniques that areimplemented in system 10 may be applied, mutatis mutandis, in gatedmapping of other physiological parameters, such as temperature orchemical activity, both in the heart and in other organs. Alternativelyor additionally, as mentioned above, contact gating may be used togather coordinate points (without necessarily measuring otherparameters) for use in physical mapping of the surface or volume of abody cavity.

The corresponding structures, materials, acts, and equivalents of allmeans or steps plus function elements in the claims below are intendedto include any structure, material, or act for performing the functionin combination with other claimed elements as specifically claimed. Thedescription of the present disclosure has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimiting to the disclosure in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the disclosure. Theembodiment was chosen and described in order to best explain theprinciples of the disclosure and the practical application, and toenable others of ordinary skill in the art to understand the disclosurefor various embodiments with various modifications as are suited to theparticular use contemplated.

It is intended that the appended claims cover all such features andadvantages of the disclosure that fall within the spirit and scope ofthe present disclosure. As numerous modifications and changes willreadily occur to those skilled in the art, it is intended that thedisclosure not be limited to the limited number of embodiments describedherein. Accordingly, it will be appreciated that all suitablevariations, modifications and equivalents may be resorted to, fallingwithin the spirit and scope of the present disclosure.

What is claimed is:
 1. A method of mapping a body cavity of a subjectusing a probe having a distal tip and being operatively connected to aprocessor, comprising: contacting the distal tip of the probe withtissue at a location in the body cavity of the subject causing adeflection of the distal tip, the probe having a distal end configuredfor insertion into the body cavity of the subject and further comprisinga contact force sensor including a position sensor, a first magneticfield transmitter, and a resilient member, the distal end having thedistal tip and an electrode, the electrode configured to acquirephysiological electrical activity in tissue; generating one or morefirst signals with the position sensor and the first magnetic fieldtransmitter of the contact force sensor indicative of the deflection ofthe distal tip resulting from a contact pressure exerted on the tissueby the distal tip, and transmitting the one or more first signals to theprocessor; generating one or more second signals with the positionsensor and a second magnetic field transmitter, the one or more secondsignals distinguishable from the one or more first signals andindicative of location and orientation coordinates of the distal end ofthe probe, and transmitting said one or more second signals to theprocessor; in the processor, measuring the deflection of the distal tipat the location and calculating a respective contact pressure betweenthe probe and the tissue in the body cavity at the location using theone or more first signals; rejecting the one or more first signals forwhich the respective contact pressure is outside a defined range; in theprocessor, automatically collecting a map point only when the calculatedrespective contact pressure is below a predetermined threshold, the mappoint including coordinate reading from the position sensor responsiveto the second magnetic field transmitter; creating or updating a map ofa volume of the body cavity using the map point for the one or morefirst signals that are not rejected; and wherein the processor furtherconfigured to display the map of the volume of the body cavity.
 2. Themethod according to claim 1, wherein the body cavity comprises a chamberof a heart.
 3. The method according to claim 1, wherein rejecting theone or more first signals comprises rejecting the one or more firstsignals when the contact pressure is above a predetermined upper bound.4. The method according to claim 1, wherein the defined range rangesbetween 5 and 35 grams.
 5. The method according to claim 1, furthercomprising converting the map of the volume into a surface map.
 6. Themethod of claim 5, wherein the converting the map of the volume into asurface map includes finding and linking outer points of the volume. 7.The method of claim 1, further comprising repositioning the probe whenthe one or more first signals are rejected.
 8. The method of claim 1,further comprising providing a visual feedback to reposition the probewhen the one or more first signals are rejected.
 9. Apparatus formapping, comprising: a probe, having a distal end configured forinsertion into a body cavity and further comprising a contact forcesensor including a position sensor, a first magnetic field transmitter,and a resilient member, the distal end having a distal tip and anelectrode, the electrode being configured to acquire physiologicalelectrical activity in tissue; wherein the distal tip of the probe isconfigured to contact tissue in the body cavity and deflect, theposition sensor and the first magnetic field transmitter of the contactforce sensor are configured to generate one or more first signals fromthe position sensor and the first magnetic field transmitter indicativeof the deflection of the distal tip resulting from a contact pressureexerted on tissue in the body cavity by the distal tip and transmit saidone or more first signals to a console, and the position sensorresponsive to a second magnetic field transmitter is configured togenerating one or more second signals indicative of location andorientation coordinates of the distal end of the probe and fortransmitting said one or more second signals to the console, the one ormore second signals distinguishable from the one or more first signals;and wherein the console including a processor, which is configured to:receive the one or more first signals, the one or more second signals,process the one or more second signals for determining the location andorientation coordinates of the distal end of the probe at the location,process the one or more first signals to measure the deflection of thedistal tip at the location and calculate the contact pressure exerted onthe tissue by the distal tip, automatically reject one or more firstsignals for which the respective contact pressure is outside a definedrange, and automatically collect a map point only when the calculatedcontact pressure for which the respective contact quality is below apredetermined threshold, and to create or update a map of a volume ofthe body cavity using the map point for the one or more first signalsthat are not rejected, the map point including coordinate reading fromthe position sensor responsive to the second magnetic field transmitter;and wherein the processor is further configured to display the map ofthe volume of the body cavity.
 10. The apparatus according to claim 9,wherein the body cavity comprises a chamber of a heart.
 11. Theapparatus according to claim 9, wherein the processor is furtherconfigured to reject the one or more first signals when the contactpressure is above a predetermined upper bound.
 12. The apparatusaccording to claim 9, wherein the defined range ranges between 5 and 35grams.
 13. The apparatus according to claim 9, wherein the processor isfurther configured to convert the map of the volume into a surface map.14. The apparatus of claim 13, wherein the processor is furtherconfigured to convert the map of the volume into a surface map byfinding and linking outer points of the volume.
 15. The apparatus ofclaim 9, further wherein the processor is further configured toreposition the probe when the one or more first signals are rejected.16. The apparatus of claim 1, further wherein the processor is furtherconfigured to provide a visual feedback signal to reposition the probewhen the one or more first signals are rejected.